The subject matter disclosed herein relates to turbines and, in particular, to late lean injection systems associated with gas and steam turbines.
Currently, some gas turbine engines fail to operate at high efficiencies and produce undesirable air polluting emissions. The primary air polluting emissions usually produced by turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide and unburned hydrocarbons. Since oxidation of, e.g., molecular nitrogen in gas turbine engines is dependent upon a high temperature in the combustor and the residence time for the reactants at the high temperature within the combustor, a level of thermal NOx formation is reduced by maintaining the combustor temperature below the level at which thermal NOx is formed or by limiting the residence time for the reactants at the high temperatures such that there is insufficient time for the NOx formation reactions to progress.
One temperature controlling method involves the premixing of fuel and air to form a lean mixture thereof prior to combustion. However, it has been seen that, for heavy duty industrial gas turbines, even with the use of premixed lean fuels, the required temperatures of the combustion products are so high that the combustor must be operated with peak gas temperatures in the reaction zone that exceed the thermal NOx formation threshold temperature, resulting in significant NOx formation.